msm: vidc: Use internal size for extradata plane

Derive extradata plane size using internal MACRO rather
than getting from Venus. This helps to keep clients and
driver in sync.

CRs-Fixed: 1011881
Change-Id: I2b3536f5eb2742d6b6855140c40724f6425d1578
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>